I was going to post this in my grow adventures however I feel that the info I have from today is a good start as I understand that not alot of people use light meters. I know its not the end all yet but it is the starting line. We have all heard that COBs can out preform any other light in the efficiency area. While I agree and have seen many results.... I trust no one. So I finally got my (cheap HydroFarm) PAR meter in the mail today (if anyone knows where the calculation adjustments are for the meters let me know) From most of the videos Ive seen there isnt much difference between all of the different meters.. Just search youtube. That brings me to the PPFD results (aka the only ones that mater) for the HPS, DE HPS, and COBS. All of these tests were in a 5x4 area and the light was 2ft exactly away. I measured every square foot. (I plan on doing more in a 4x4 but I have to rebuild the COBS for that.) 2 of the sides had reflection for all tests. (in a corner) SO here are the numbers that I got out of this 2ft distance DE HPS 1000W GROW STATION 4x5 1ST ROW 250 450 586 414 200 2ND ROW 270 630 1080 689 249 3RD ROW 280 648 1100 598 232 4TH ROW 204 362 408 325 170 457.25PPFD 1000W HPS 8in HOOD REFLECTOR 4x5 1ST ROW 176 357 443 324 158 2ND ROW 240 554 720 504 264 3RD ROW 260 645 816 600 270 4TH ROW 198 270 320 253 140 375.55PPFD BARE COB LED IN A 5x5 800W ROW 1 270 425 530 450 430 ROW 2 390 460 560 445 421 ROW 3 400 470 584 463 427 ROW 4 330 435 563 454 424 329.65 PPFD Seems like an open and shut DE HPS win huh? I mean what could make anything change? Except that everything was at 2ft. After seeing what Im getting I can run around 1ft away with the COBS bare. And in the next test Ill be testing everything in a 4x4 at the preferred height. Stay tuned if you like, or let me know if you see any errors. This will be a grow between all of the lights as soon as I find a 4th strain. ( my purple guy isnt close to done with his new strain) The difference between this thread and my Adventures thread id that this is specifically metric based and the other is more of a results/ what Im dealing with and build log.